1. Field of the Invention
The invention relates to a solenoid stator assembly for an electromechanically actuated fuel injector and, more particularly, to a solenoid stator assembly with a reinforcement structure.
2. Background Art
Conventional solenoid stator assemblies for electromechanically actuated fuel injectors include a stator core with a stator coil for developing a magnetic force upon an armature of a fuel injector. The armature is typically part of a valve assembly for regulating the flow of fuel to an injector nozzle. The solenoid stator assembly commonly includes a housing formed of an electrically insulating material for enclosing the stator core and the stator coil. Electrical terminals, which extend into the housing, are connected to an input lead and an output lead for the stator coil.
Electrical current under the control of an electronic engine controller is distributed to the stator coil for controlling injection timing and fuel metering by the valve assembly. Fuel passing through the valve assembly during a fuel injection pulse is pressurized at a high injection nozzle pressure. Fuel passing through the valve assembly between injection pulses, which is referred to as spill fuel flow, is substantially lower than nozzle injection pressure. The stator assembly, particularly the stator housing, is in contact with the lower pressure spill flow, but the spill flow pressure still is sufficiently high to cause undesirable pressure loading. The pressurized fuel may seep between the core and the housing, thus pressurizing and deforming the housing. Continued pressure applied to the stator assembly may cause the housing to fatigue, fracture, or separate from the core.
Since the solenoid stator assembly is used in fuel injectors for motor vehicles, it may experience also large changes in temperature. Due to differing rates of thermal expansion of the materials used in injectors, the solenoid stator assembly may experience thermal loading, which may exacerbate separation of the housing from the stator core. Further, the solenoid stator assembly may undergo cavitation erosion caused by fluid dynamics associated with the reciprocating armature.
Prior art solenoid stator assemblies have attempted to overcome these difficulties with various degrees of success. For example, U.S. Pat. No. 5,155,461, which is assigned to assignee of the present invention, discloses a preloaded solenoid stator assembly to overcome the loads encountered during use. The '461 patent also discloses a stator core having a plurality of external configurations for bonding with an over-molded polymer housing.
Attempts have been made using other prior art solenoid stator assemblies to improve robustness by providing an external housing or band, typically metallic, about an insulated housing. An example of a design of this type is disclosed in U.S. Pat. No. 5,339,063 issued to Pham. Another prior art reference, U.S. Pat. No. 5,926,082, issued to Coleman et al., discloses a reinforcement band disposed about the lower end of a stator housing.
Although the prior art references disclose various solenoid stator assemblies that are structurally enhanced to overcome mechanical and hydraulic loads, they generally are costly due to complex manufacturing processes required and the special materials needed.